Depth Tweak and tuning

tunes reduction related parameters, and introduces more reduction on found good moves.

credit for this patch goes also to candirufish Yoshie2000 dubslow peregrineshahin Vizvezdenec

Passed STC:
LLR: 2.94 (-2.94,2.94) <0.00,2.00>
Total: 38424 W: 10346 L: 10040 D: 18038
Ptnml(0-2): 103, 4111, 10473, 4427, 98
https://tests.stockfishchess.org/tests/view/642ca74277ff3301150db511

Passed LTC:
LLR: 2.97 (-2.94,2.94) <0.50,2.50>
Total: 136968 W: 37151 L: 36660 D: 63157
Ptnml(0-2): 43, 13052, 41808, 13533, 48
https://tests.stockfishchess.org/tests/view/642d632377ff3301150dddbe

closes https://github.com/official-stockfish/Stockfish/pull/4499

bench: 3672914

diff --git a/src/search.cpp b/src/search.cpp
index aa1a3e8c17fec2a39407c3753e95338e9cd5d443..fba9685b2e035deaef896e501841e450057eb51d 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -72,7 +72,7 @@ namespace {
 
   Depth reduction(bool i, Depth d, int mn, Value delta, Value rootDelta) {
     int r = Reductions[d] * Reductions[mn];
-    return (r + 1449 - int(delta) * 1001 / int(rootDelta)) / 1024 + (!i && r > 941);
+    return (r + 1449 - int(delta) * 937 / int(rootDelta)) / 1024 + (!i && r > 941);
   }
 
   constexpr int futility_move_count(bool improving, Depth depth) {
@@ -82,7 +82,7 @@ namespace {
 
   // History and stats update bonus, based on depth
   int stat_bonus(Depth d) {
-    return std::min(341 * d - 470, 1855);
+    return std::min(341 * d - 470, 1710);
   }
 
   // Add a small random component to draw evaluations to avoid 3-fold blindness
@@ -775,7 +775,7 @@ namespace {
     // Step 7. Razoring (~1 Elo).
     // If eval is really low check with qsearch if it can exceed alpha, if it can't,
     // return a fail low.
-    if (eval < alpha - 426 - 252 * depth * depth)
+    if (eval < alpha - 426 - 256 * depth * depth)
     {
         value = qsearch<NonPV>(pos, ss, alpha - 1, alpha);
         if (value < alpha)
@@ -797,7 +797,7 @@ namespace {
         && (ss-1)->statScore < 18755
         &&  eval >= beta
         &&  eval >= ss->staticEval
-        &&  ss->staticEval >= beta - 19 * depth - improvement / 13 + 253 + complexity / 25
+        &&  ss->staticEval >= beta - 20 * depth - improvement / 13 + 253 + complexity / 25
         && !excludedMove
         &&  pos.non_pawn_material(us)
         && (ss->ply >= thisThread->nmpMinPly || us != thisThread->nmpColor))
@@ -805,7 +805,7 @@ namespace {
         assert(eval - beta >= 0);
 
         // Null move dynamic reduction based on depth, eval and complexity of position
-        Depth R = std::min(int(eval - beta) / 168, 6) + depth / 3 + 4 - (complexity > 825);
+        Depth R = std::min(int(eval - beta) / 172, 6) + depth / 3 + 4 - (complexity > 825);
 
         ss->currentMove = MOVE_NULL;
         ss->continuationHistory = &thisThread->continuationHistory[0][0][NO_PIECE][0];
@@ -1333,16 +1333,18 @@ moves_loop: // When in check, search starts here
 
               if (PvNode && value < beta) // Update alpha! Always alpha < beta
               {
-                  alpha = value;
 
                   // Reduce other moves if we have found at least one score improvement (~1 Elo)
                   if (   depth > 1
-                      && depth < 6
-                      && beta  <  10534
-                      && alpha > -10534)
-                      depth -= 1;
+                      && ((improving && complexity > 971) || (value < (5 * alpha + 75 * beta) / 87) || depth < 6)
+                      && beta  <  12535
+                      && value > -12535) {
+                      bool extraReduction = depth > 2 && alpha > -12535 && bestValue != -VALUE_INFINITE && (value - bestValue) > (7 * (beta - alpha)) / 8;
+                      depth -= 1 + extraReduction;
+                  }
 
                   assert(depth > 0);
+                  alpha = value;
               }
               else
               {